1. Field of the Invention
The present invention relates to an optically reflecting code plate to be used with a rotary encoder of optical type, for example, and to a pattern layout of the code plate.
2. Description of the Prior Art
The rotary encoder of optical type is constructed of a code disc, which is formed alternately with a number of slit-shaped reflective and unreflective portions on the surface of a substrate in the circumferential direction, and a sensor head which is composed of an light emitting element and a light receiving element and which is arranged to face the surface of the code plate.
Before entering into detailed description of the present invention, cursory review will be made upon the background of the code disc of the present invention.
FIG. 1 is a side elevation showing a motor which is equipped with the rotary encoder, and FIG. 2 is a top plan view showing the code disc which is used in the rotary encoder.
On the drive shaft 2 of a motor 1, there is fixed a code disc 3 which is made rotatable together with the drive shaft 2. The code disc 3 is formed in the vicinity of its outer circumference, as shown in Fig. 2, with a number of slit-shaped white reflective portions 4 and black unreflective portions 5 which are arranged regularly and alternately in the circumferential direction. Reverting to FIG. 1, a sensor head 6 is arranged at a position to face the surface of the code disc 3 formed with those reflective and unreflective portions 4 and 5. That sensor head 6 is equipped with at least one light emitting element 7 such as an LED and a light receiving element 8 such as a photo transistor. The beam emitted from the light emitting element 7 is reflected by the reflective portions 4 so that the reflected beam is received by the light receiving element 8. If the beam irradiates the unreflective portions 5, on the contrary, it does not come into the the light receiving element 8. By counting the number of times of beam receptions of the light receiving element 8, therefore, it is possible to control the angle of rotation of the motor and to detect the r.p.m. of the same.
In order to enhance the detecting sensitivity of the rotary encoder thus constructed, the code disc 3 has to be formed with such a pattern as to reflect and absorb the beam highly efficiently and accurately. Especially, if the code disc 3 is reduced in diameter or if the slit widths are narrowed in accordance with the increase in the number of the reflective and unreflective portions 4 and 5, it becomes difficult to conduct the optical reflection and absorption highly efficiently and accurately.